1878.] 



of the Motor Area of the Brain. 



39 



Types of Structural Lamination. 



Meynert enumerates five distinct plans, according to which the 

 various layers of the cortex are disposed, of which the more extensive 

 formation is his five-laminated type, which he regards as that charac- 

 teristic of the cortex of the vault and a portion of the gyrus f ornicatus.* 

 It is with regard to this type of structural lamination that the observa- 

 tions now to be recorded deal ; and it is hoped that they will tend not 

 only to point out how errors have crept into the descriptions of some 

 writers, but also to reconcile conflicting^ opinions upon this subject. 

 We regard the ascending frontal convolution as affording the most 

 suitable representation of the typical lamination of the motor area, and 

 our descriptions, therefore, apply more directly to this region than to 

 the remaining gyri at the vertex. 



It is premised that at least one authority of note, Baillarger, differs 

 from Meynert in his description of this type of lamination, enumerating 

 the layers as six in number, whilst Meynert notices five only. 



Typical Lamination of the Motor Area. 

 The following description of the lamination of cellular elements in 

 the ascending frontal convolution will suffice to convey the result of 

 our observations. 



First Layer. — A pale narrow band, extremely delicate and friable, is 

 seen in sections to form the extreme limit of the cortical layers. The 

 histological tissues composing this formation are connective, nervous, 

 and vascular. The connective does not differ essentially from that 

 universally present as the basis of the cortical substance. It consists of 

 minute fibrils, interlacing, anastomosing, and forming, by an intricate 

 plexiform arrangement, a dense felt-like bed, possessing great powers 

 of_ elastic distension. In the areola betwixt these fibrils, a finely mole- 

 cular base may be detected, which appears greatly altered by the 

 employment of various reagents. In this matrix distinct connective 

 cells are observed, including one or more nuclei within an investment 

 of most delicate protoplasm, and from which, when seen under favour- 

 able circumstances, numerous minute branches radiate into the sur- 

 rounding neuroglian network. In sections obtained from preparations 

 hardened by chromic acid two forms of cellular elements are observed : 



(a.) Cells that in diameter vary from 6/t to 9/ll, the delicate proto- 

 plasm of which is almost invariably shrunken up or destroyed by the 

 re-agents employed, appearing, therefore, like free nuclei, except when 

 examined by fresh methods of preparation. These elements assume 

 the direction taken by the vessels of the cortex, and frequently are 

 seen in large numbers along the perivascular sheaths. 



(b.) Larger cells, ranging in diameter up to 13/*, with a similarly 



* " The Brain of Mammals." By Theodore Meynert (Strieker's Human and Com- 

 parative Histology, vol. ii, p. 381). 



